Method of treating selenium elements



Aug. 15, 1944. o. SASLAW 2,356,094

METHOD OF TREATING SELENIUM ELEMENTS Filed Feb. 11, 1943 INVENTOR.

0TTO SASLAW Patented Aug. 15, 1944 METHOD or TREATING SELENIUM ELEMENTS om Saslaw. Lyndhurst, N. 1., assinior to Federal Telephone 8; Radio Corporation, New N. Y., a corporation of Delaware York,

Application February 11, 1943, Serial No. 475,569

Claims.

This invention relates to selenium elements and has for its object to reclaim or improve the qualities and characteristics of selenium elements which have been rejected or are below a desired standard.

Selenium elements such as rectifiers are commonly made by placing an adherent layer of selenium on a carrier plate and heat treating'the selenium to crystallize it; and the selenium might if desired be subjected to other treatments. The selenium surface is then covered with a counterelectrode, ordinarily placed on it by means of a metal spray such as Woods metal which when hardened forms a conducting surface. The selenium element is then commonly electroformed I by connecting it in a D. C. or pulsating D. C. circuit with the counterelectrode connected to one lead and the carrier plate to the other. The element will then exhibit the well known rectifying characteristic of transmitting more current in one direction than in the other. Such rectifier elements may vary somewhat in their qualities, the factors by which they are judged commonly being the conductivity in the forward current direction and the resistivity in the reverse current direction. It is usually desired that the rectifier have a high forward conductivity and has high as possible a ratio of forward to reverse direction current. Such rectifiers are commonly rejected for having too high a reverse current.

In accordance with my invention I am enabled to reclaim a large number of such rejected elements and to improve thereverse resistance so that the reverse current will drop to a desired low value in operation. I carry out this improvement by steaming the disks and then electroforming them in a manner well understood in the art by subjecting them to a direct current.

In the drawing, Fig. 1 is a face view of a selenium rectifier element showing the several layers of material broken away and Fig. 2 is a side sectional view taken at line 2-2 of Fig. 1.

The base or carrier plate I is ordinarily a plate or disk of metal which may be of aluminum or iron or steel or may be nickel plated if desired.

.This may if desired be provided with a central hole 5 as shown. The surface of this plate is commonlyproughened and there is then applied to it in a well known manner a layer 2 of selenium. This may for example be applied by melting selenium powder and spreading it over the surface and then allowing it to cool, which leaves an adherent layer of vitreous selenium. This is treatment to crystallize the selenium and this may be carried out in a well known way by applying pressure against the elements while heating the selenium to a temperature in the order of for example 120 for a short time, after which the temperature may be raised to around 200 without any pressure. Other well known treatments may be given to selenium and as they constitute no part of this invention they are not discussed here. The selenium is then commonly provided with a counterelectrode layer 4 which may be put on by spraying the selenium surface with a substance such as Woods metal after first masking the outer margin and also the margin around the central'hole in order to prevent short circuiting of this counterelectrode to the hue plate.

When a disk or selenium element of the foregioing type is considered to have too high a reverse current I treat it in accordance with my invention by steaming it. This may be done by dipping it in a container of steam. Only a short time of steam treatment is required, for example voltage source and the carrier electrode to they The D. C. voltage source may be' other terminal. for example that delivered by a half wave or full wave rectifier, and may be around 20 volts. This electroforming may be carried out for a period of time which may vary anywhere from a half hour to several hours, which will enable the disk properly to operate as a rectifier.

I have found that many selenium rectifier elements which have been found to have too high a reverse current in operation can be reclaimed and made to have a smaller reverse current by steaming and electroforming in accordance with my invention.

then commonly subjected to a heat and pressure 66 What is claimed is:

1. The method of treating a selenium element comprising a selenium layer adhering to a base plate and covered by a counterelectrode,

which comprises steaming the element and then electroforming it by a pulsating D. C. voltage. 2. The method of treating a selenium rectifier element which comprises steaming it and then electroi'orming it.

3. The method of treating a selenium rectifier element which comprises steaming it for a period of about 30 seconds and then electroforming it while it is still moist.

4. The method of treating a selenium element having a selenium layer sandwiched between a carrier plate and a counterelectrode which comprises steaming the element and then electroi'orming it while still moist.

5. The method of treating a selenium element having a selenium layer sandwiched between a 5 carrier plate and a counterelectrode which comprises steaming the element, then rinsing it in water and then electroformins it while still moist.

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